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Resist class

DNQ–novolak positive resists

—01 / Definition

What it is

DNQ–novolak resists are positive photoresists built on a novolak (phenol-formaldehyde) resin loaded with a diazonaphthoquinone (DNQ) dissolution inhibitor; exposure converts the DNQ where light lands into a species that dissolves readily in developer, so the exposed pattern washes away and the unexposed resist remains. The AZ family, Microposit/Kayaku S1800 series, Allresist AR-P and SPR-series resists are all built on this chemistry.

—02 / Mechanism

How it patterns

novolak+DNQ365 / 405 nmexposedevelop
Unexposed film: novolak + DNQ dissolution inhibitor. Exposure at 365/405 nm converts the DNQ via a Wolff rearrangement into a developer-soluble acid. Develop clears the exposed region, leaving the unexposed pattern — positive tone.

The DNQ dissolution inhibitor

Unexposed, the novolak resin alone would already dissolve at a modest rate in an aqueous developer; the DNQ compound dispersed through it acts as a dissolution inhibitor, suppressing that rate by roughly two orders of magnitude so the unexposed film survives development largely intact. The resist's contrast comes almost entirely from removing that inhibition selectively where the mask (or, on a maskless tool, the exposure pattern) lets light through.

Exposure: a Wolff rearrangement, not amplification

At 365 nm or 405 nm, the DNQ absorbs a photon and loses nitrogen in a Wolff rearrangement, forming a ketene intermediate that reacts with trace water in the film to yield an indenecarboxylic acid. That acid is itself soluble in the aqueous-base developer and, more importantly, removes the parent DNQ's inhibiting effect on the novolak around it — so the exposed region's dissolution rate rises sharply. This is a direct photochemical conversion consumed stoichiometrically by the light dose, rather than a catalytic photoacid amplification, which is why DNQ-novolak resists need no post-exposure-bake deprotection step to develop and are relatively insensitive to post-exposure delay.

Develop: the positive tone

Development in an aqueous base — historically KOH, now almost universally metal-ion-free TMAH — dissolves the exposed, deinhibited region far faster than the still-inhibited unexposed film, so the pattern that survives is the unexposed pattern: the definition of positive tone. Because the underlying chemistry is a direct photoreaction rather than a diffusing catalyst, the exposed/unexposed contrast is set mostly by the optical dose profile, which is part of why these resists have long been the default for micron-scale mask-aligner and stepper work.

Standing waves and the swing curve

Because the substrate reflects the exposing light back into the film, the standing wave formed between the incident and reflected beams modulates the dose with depth, printing faint horizontal ridges on the sidewall and making the resist's effective sensitivity oscillate with coating thickness (the swing curve) — a datasheet's recommended thickness values sit at a swing-curve minimum for that reason. A post-exposure bake diffuses the photoproduct enough to average out the ridges, and an underlayer or a longer wavelength shift can flatten the swing curve further; some AZ-family products are also formulated for a controlled partial image reversal, a separate process built on the same DNQ chemistry that this page does not re-derive (see the image-reversal resist page).

—03 / Strengths & limits

Where it fits

Strengths
  • For micron-scale positive patterning with wide process latitude, DNQ–novolak resists give predictable, well-characterized contrast across a broad exposure-dose window, which is why decades of mask-aligner and stepper processes are built around them.
  • For an aqueous-developer process line, DNQ–novolak resists develop in a metal-ion-free TMAH base, the same developer family used across most positive resists in a cleanroom.
  • For same-day iteration without a fresh photoacid-generator batch to manage, DNQ–novolak resists are comparatively insensitive to post-exposure delay, since the photoreaction is direct rather than catalytic.
Limits
  • For deep-sub-micron critical-dimension control, DNQ–novolak resists are a poor fit — a direct, non-catalytic photoreaction gives less resolution latitude than that regime demands.
  • For very thick single-coat films, DNQ–novolak resists are typically spun in the sub-10-micrometre range per coat; a much thicker mould or plating form is better served by a resist chemistry built for that regime.
  • For a process where standing-wave sidewall ridges cannot be tolerated, the swing curve has to be managed deliberately — via coating thickness, an underlayer, or a post-exposure bake — rather than assumed away.
—04 / Recipes in this class

Datasheet-cited recipes

Every value on these pages is cited to the manufacturer’s datasheet — spin curve, bake schedule, exposure dose and developer.

AR-P 3510T2 µm · DNQ-novolakAR-P 53501 µm · DNQ-novolakAZ 10XT4–20 µm · DNQ-novolakAZ 15050.6–1.6 µm · DNQ-novolakAZ 15121.4–3.9 µm · DNQ-novolakAZ 15181.9–5.6 µm · DNQ-novolakAZ 45332.7–4.7 µm · DNQ-novolakAZ 5214E1.1–2.0 µm · DNQ-novolakAZ 92607.9–11.4 µm · DNQ-novolakAZ ECI 30070.6–1.1 µm · DNQ-novolakAZ ECI 30121.1–1.9 µm · DNQ-novolakAZ ECI 30272.4–4.4 µm · DNQ-novolakAZ P46206.9–14.8 µm · DNQ-novolakKemLab KL 5300 series0.1–2.5 µm · DNQ-novolakKemLab KL IR 151.2–2.6 µm · DNQ-novolakma-P 12151.5 µm · DNQ-novolakma-P 1275G9.3–60 µm · DNQ-novolakMegaposit SPR 220-3.02.3–4.6 µm · DNQ-novolakMegaposit SPR 220-7.05.5–52 µm · DNQ-novolakMicroposit S1805— · DNQ-novolakMicroposit S1818— · DNQ-novolakS18131.0–1.9 µm · DNQ-novolakS1822— · DNQ-novolak

See all in the library →

—05 / Family references

Further reading

  1. F. H. Dill, W. P. Hornberger, P. S. Hauge, J. M. Shaw. Characterization of positive photoresist. IEEE Transactions on Electron Devices (1975). doi:10.1109/t-ed.1975.18159
  2. J. Pacansky, J. R. Lyerla. Photochemical Decomposition Mechanisms for AZ-Type Photoresists. IBM Journal of Research and Development (1979). doi:10.1147/rd.231.0042
  3. E. J. Walker. Reduction of photoresist standing-wave effects by post-exposure bake. IEEE Transactions on Electron Devices (1975). doi:10.1109/t-ed.1975.18162
—06 / FAQ

Common questions

What makes a DNQ-novolak resist positive-tone?

Exposure converts the DNQ dissolution inhibitor into a developer-soluble acid, so the exposed region dissolves away in the developer and the unexposed resist remains — the pattern that survives is the unexposed pattern, the definition of a positive tone.

What is the DNQ dissolution inhibitor?

DNQ (diazonaphthoquinone) is a photoactive compound dispersed through the novolak resin that suppresses its dissolution rate in aqueous developer by roughly two orders of magnitude until exposure removes that inhibition; the resist's contrast comes from switching that inhibition off selectively where light lands.

Why do standing waves appear in DNQ-novolak exposures?

The substrate reflects the exposing light back into the film, and the standing wave formed between the incident and reflected beams modulates the dose with depth, printing faint sidewall ridges and making the resist's effective sensitivity oscillate with coating thickness (the swing curve) — which is why datasheets specify a thickness at a swing-curve minimum and why a post-exposure bake helps average the effect out.

Expose it at 365 and 405 nm

NANYTE BEAM is a desktop maskless lithography system with software-selectable dual-wavelength exposure and 16-bit grayscale — no photomask, no mask cost, same-day iteration.

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General photolithography reference material, not a specification of any particular NANYTE BEAM configuration. Product names and trademarks belong to their respective owners; NANYTE is not affiliated with the manufacturers mentioned.